Characterization of SCP-2 from Euphorbia lagascae reveals that a single Leu/Met exchange enhances sterol transfer activity

FEBS J. 2006 Dec;273(24):5641-55. doi: 10.1111/j.1742-4658.2006.05553.x.

Abstract

Sterol carrier protein-2 (SCP-2) is a small intracellular basic protein domain implicated in peroxisomal beta-oxidation. We extend our knowledge of plant SCP-2 by characterizing SCP-2 from Euphorbia lagascae. This protein consists of 122 amino acids including a PTS1 peroxisomal targeting signal. It has a molecular mass of 13.6 kDa and a pI of 9.5. It shares 67% identity and 84% similarity with SCP-2 from Arabidopsis thaliana. Proteomic analysis revealed that E. lagascae SCP-2 accumulates in the endosperm during seed germination. It showed in vitro transfer activity of BODIPY-phosphatidylcholine (BODIPY-PC). The transfer of BODIPY-PC was almost completely inhibited after addition of phosphatidylinositol, palmitic acid, stearoyl-CoA and vernolic acid, whereas sterols only had a very marginal inhibitory effect. We used protein modelling and site-directed mutagenesis to investigate why the BODIPY-PC transfer mediated by E. lagascae SCP-2 is not sensitive to sterols, whereas the transfer mediated by A. thaliana SCP-2 shows sterol sensitivity. Protein modelling suggested that the ligand-binding cavity of A. thaliana SCP-2 has four methionines (Met12, 14, 15 and 100), which are replaced by leucines (Leu11, 13, 14 and 99) in E. lagascae SCP-2. Changing Leu99 to Met99 was sufficient to convert E. lagascae SCP-2 into a sterol-sensitive BODIPY-PC-transfer protein, and correspondingly, changing Met100 to Leu100 abolished the sterol sensitivity of A. thaliana SCP-2.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Arabidopsis / chemistry
  • Arabidopsis / genetics
  • Arabidopsis / metabolism
  • Biological Transport / genetics
  • Boron Compounds / chemistry
  • Carrier Proteins / chemistry
  • Carrier Proteins / genetics*
  • Carrier Proteins / metabolism*
  • Euphorbia / genetics*
  • Gene Expression Regulation, Plant
  • Germination
  • Models, Biological
  • Models, Molecular
  • Molecular Sequence Data
  • Molecular Structure
  • Mutagenesis, Site-Directed
  • Palmitic Acid / chemistry
  • Palmitic Acid / metabolism
  • Phosphatidylcholines / chemistry
  • Phosphatidylcholines / metabolism
  • Phosphatidylcholines / pharmacokinetics
  • Plant Proteins / chemistry
  • Plant Proteins / genetics*
  • Plant Proteins / metabolism*
  • Protein Conformation
  • Seeds / enzymology
  • Sequence Alignment
  • Sterols / chemistry
  • Sterols / metabolism*

Substances

  • 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene
  • Boron Compounds
  • Carrier Proteins
  • Phosphatidylcholines
  • Plant Proteins
  • Sterols
  • sterol carrier proteins
  • Palmitic Acid